How do you think they talk to submarines? (the answer is: slowly!) You
can pass RF through water (even sea water), but unless it's very low
frequency (or extremely low - ELF) it doesn't get very far. You'd get
serious attenuation with 10s of MHz.
AFAIK VLF (3-20kHz) is only used near the surface with a trailing
antenna, but the latest ELF systems have neither requirement. What I
can find on the ELF system in use by the US (76Hz) suggests they can
receive ELF at operational speed and depth, which doesn't suggest
"near the surface" to me. It's all relative of course and hard figures
are hard to come by (hardly surprising!), but I've seen 2-300m
mentioned. AIUI they use on/in-hull antennas (presumably SQUID based)
instead of trailing wire antennas for ELF too.
OK, perhaps it's not how they /usually/ talk to submarines though :)
You're damn right it does. (The intuitive notion of a tight relationship
between bit rate and analog bandwidth disappears like parted waters if you
study communication theory -- you can have data rates far greater or far
less than bandwidths, in exchange for requirements for SNR or other
constraints.) But the subject tends to the counterintuitive, so it
collects notions and suppositions and opinions. (Like various other areas
of electronics.) This by the way is partly the domain of the newsgroup
Is this why QAM 256 is far better than simple modulation schemes?
I mean it allows for so much more *use* of the signal as it is being
Anyway, this is party why one can get so many more channels per
transponder on a comm bird than was available in the past. That 6MHz
wide channel is being filled to the brim with data (and that data
compressed as well), as opposed to the signals they repeated in the
60s and 70s.
Thank God for General Instrument (now a division of Motorola).
They (along with others) brought you wide screen form factors,
MPEG-2, and HDTV. As well as twelve channel per carrier uplink
encoding and decoding. They made your Video/TV life over ten times
GI was not just another cable box maker.
Then the Cable Cos ream us up the ass with their pricing. All the
while letting their hardware age, and fester, instead of keeping up.
They call that "a good value service".
Cox's news server is one fine example. I'd be surprised if it is
even one terabyte in archive size.
On Thu, 13 May 2004 23:15:17 -0500, "Dave VanHorn"
Motorola only bought the uplink encoder division from what I know...
which is not exactly what happened... :]
GI has been around for decades, they bought the encoder division
which was formerly an arm of Titan/ Linkabit. Or was them.
Anyway... thank them and Woo Paik in particular (now in S. Korea as
Pres of his own company) specifically for HDTV in digital form. Were
it not for them, the idiots in the consortium would have made an
analog version... Oh boy.
A teacher at my college told me that somewhere (i cant have been listening)
they use the granite rock as an antenna, and then drill down however amny
miles apart and make a connection.
not sure if he was talking aout of his...
(Amazon.com product link shortened)
I just picked up this one, having read "blind man's bluff" recently.
The chapter on "Hunt for Red October" was rather chilling, as I was living
in Hawaii at the time.
On Wed, 12 May 2004 04:36:27 GMT, "The other John Smith"
This reminds me of another example of the extreme end of
communications theory. A couple years ago I interviewed with a
company that makes remote readable electric meters. They put a
module in the bottom of the meter that reads and counts the
rotation of the disk and sends a signal back to equipment placed
at certain places around the power grid to collect meter
The signals were sent over the power grid in a band of something
like 10 or 20 Hz centered around 60 Hz so it could get through
transformers. They crammed thousands of parallel data channels
hundredths of a Hz apart into that band. Time to transmit ONE
BIT was something like 20 minutes.
They claimed in testing they had received the signal up to 100
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